Proposed is a continuation of a study of the hormonal control of the commitment of the insect epidermal cell to either larval or pupal differentiation. Ecdysone in the absence of juvenile hormone either in vivo or in vitro changes the commitment of the larval epidermis to pupal; the addition of juvenile hormone prevents this change. Thus, this system can be used to study the biochemical events occurring during this permanent change in cellular commitment and also to learn more about the mode of the morphogenetic action of juvenile hormone. The changes in RNA and protein synthetic patterns at this time and during both larval and pupal cuticle formation are being studied. Hybridization analysis of the changes in RNA populations is also underway. The action of juvenile hormone in controlling pigmentation during a larval molt is being studied, both its control of ommochrome synthesis by the epidermis and of the melanization of the larval cuticle. The relationship between the epidermal pigments and the tanning of pupal cuticle in vitro will also be explored.